BRISBANE, Australia - The influenza virus has hit Australia hard this winter, with Queensland recording the highest number of cases in the country, health experts warned on Wednesday.

The Influenza Specialist Group (ISG), which consists of medical and scientific specialists on influenza from around Australia and New Zealand, said on Wednesday that more than 5,000 cases of the H3N2 and Type B strains have already been diagnosed across Australia.

Experts are warning that there is worse to come and this is only the tip of the iceberg as thousands more cases go undiagnosed.

ISG said Queensland was the worst affected state with 2,536 diagnosed cases, while New South Wales was next with 2,391.

The infection rate for Queensland was ten percent higher than the same period a year ago, the ISG said.

Children under nine years old have been the hardest hit by the flu virus and the number of elderly people and those between 35 and 44 years old contracting the virus has also increased.

ISG Chair Dr Alan Hampson said that the fact that the H3N2 and the Type B strains hadn't been prominent in the community for the past few years could increase this season's severity.

"When we see high levels of H3N2, which is the predominant strain this season, there is significant impact, especially in high-risk groups," he said.

"Typically, we can expect to see more deaths and hospital admissions."

Hampson said people should protect themselves by regularly washing their hands, avoiding crowds and getting vaccinated.